Effects of wood ash and nitrogen fertilization on Scots pine crown biomass

The crown biomass, being one of the most susceptible components of the above-ground tree biomass, could respond positively to environmental changes and temporary increase in nutrient availability. The influence of wood ash and nitrogen fertilization on crown biomass was studied in a 40-year-old Scots pine (Pinus sylvestris L.) stand growing on a Haplic Arenosol. The 36-model trees for the crown biomass measurements were sampled for 3 growing seasons after the application of 5.0 t wood ash ha⁻¹, 180 kg N ha⁻¹, 2.5 t wood ash ha⁻¹ plus 180 kg N ha⁻¹, and control (untreated plots). The masses of the current, 1-year-old and older needles and shoots, and branches were measured. A significant influence on the current year needles and shoots was found after the application of 180 kg N ha⁻¹ or 2.5 t wood ash ha⁻¹ plus 180 kg N ha⁻¹. When wood ash was applied in combination with nitrogen, an extra response tendency of the crown growth, especially of the top and the middle sections of the crown, was determined. However, there was no short-term influence of wood ash on crown biomass growth.     

Wood ash and nitrogen influence on ground vegetation cover and chemical composition

An experiment was set up in a 38-year-old Scots pine stand (forest type Pinetum vacciniosum) on a sandy soil (Haplic Arenosol). Raw wood ash (WA) and nitrogen (N) fertilizers were applied. There were 6 treatments: (1) 1.25 t WA ha⁻¹; (2) 2.5 t WA ha⁻¹; (3) 5.0 t WA ha⁻¹; (4) 180 kg N ha⁻¹; (5) 2.5 WA t ha⁻¹ together with 180 kg N ha⁻¹; and (6) control (without ash or N). The effects on ground vegetation cover, biomass and chemistry of Pleurozium schreberi (Brid.) Mitt. were studied.The ground vegetation cover measurements were performed from the initial phase of the experiment and continued annually in all treatments. The ground vegetation biomass and the concentrations of the main plant nutrients (N, P, K, Ca and Mg) and some heavy metals (Cr, Cd, Pb, Ni, Cu and Zn) were determined in the 5.0 t WA ha⁻¹ and 180 kg N ha⁻¹ plots 2 years after the application.The study results showed a significant reduction of the moss cover after the application of wood ash, and the higher ash dose gave a higher decrease. N and wood ash applied together with N also decreased the cover of the moss. Small changes in the mean cover of the vascular plants occurred after the N application. The biomass of the moss remained unaffected. Significant increases of the P, Ca and Mg concentrations in P. schreberi were found after the application of 5.0 t WA ha⁻¹, and also higher N concentrations were obtained after N application. No wood ash influence on the heavy metal (Cd, Pb, Cr, Ni, Cu and Zn) concentrations in P. schreberi was found.     

Aboveground tree biomass in a recovering tropical sal (Shorea robusta Gaertn. f.) forest of Eastern Ghats,India

Aboveground biomass of individual tree species by component and total biomass per unit area for four different stages of a recovering tropical dry deciduous forest stands, dominated by sal (Shorea robusta Gaertn. f.) of the Eastern Ghats, India were investigated during 2001–2002. Different periods of recovering (2, 4, 6, and 10-year) forest stands (84°13′E, 20°29′N) were selected in the Kandhamal district of Orissa, India and sample trees of all species were harvested. Tree species diversity was 23, 23, 21 and 22 in 2, 4, 6, and 10-year recovering stands, respectively. Species-wise Ixora pavetta showed the highest biomass in 2 and 4-year stands while Shorea robusta in 6 and 10-year stands. Component-wise, in all species, bole–wood contribution ranged between 22.6% and 60.9%. Aboveground tree biomass, in all the stands, was dominated by Shorea robusta, which ranged between 12.68 and 231.91 Mg ha⁻¹. Total aboveground tree biomass was 30.12, 49.21, 107.54 and 261.08 Mg ha⁻¹ in 2, 4, 6 and 10-year stands, respectively.     

Eucalyptus gunnii: A possible source of bioenergy?

Eucalypts are widely grown throughout the world for timber, essential oil, fuel, biomass and cut foliage. In experiments in University College Dublin (UCD), Eucalyptus gunnii yielded an average dry weight of 4.74 kg per plant per annum, equivalent to 12.59 t dm ha⁻¹. The average calorific values of 17.60 MJ kg⁻¹ (leafy material) and 17.09 MJ kg⁻¹ (woody material) are less than the values reported for other species of Eucalyptus.     

Above-ground biomass estimation in ten tropical dry evergreen forest sites of peninsular India

The present study aims to estimate the above-ground biomass (AGB) distribution in ten 1-ha permanent plots, established in five sites each in inland and coastal tropical dry evergreen forests of peninsular India. Two linear regression equations, one using basal area (BA, Method 1) and the other using BA and height (Method 2) were followed. On using method 1, the AGB varied from 39.69 to 170.02 Mg ha⁻¹ and by method 2, it varied from 73.06 to 173.10 Mg ha⁻¹. The relationship between BA and AGB yielded a positive correlation for all the five sites of inland and coastal areas. The basic wood specific gravity of 41 tree species determined by oven-dry weight by volume, ranged from 0.46 to 0.92 g cm⁻³ for inland sites and 0.47 to 0.89 g cm⁻³ for the coastal sites. The AGB estimation obtained in this study represents a more realistic picture of biomass of tropical dry evergreen forests, because a relatively large area was sampled.     

Biomass accumulation in rapidly growing loblolly pine and sweetgum

Loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) trees, growing in International Paper Company's study of intensive management on marginal agricultural land near Bainbridge GA, were destructively sampled at the end of the sixth growing season. All trees were single family blocks of genetically superior trees planted 2.5 m apart on sub-soiled rows 3.6 m apart and grown with complete competition control. Management treatments were: control, irrigation, irrigation plus fertilization, and irrigation plus fertilization plus pest control. Tree measures were basal diameter, DBH, height of live crown, diameter at base of live crown, and total height. Twenty trees of each species were destructively sampled. Stems were sectioned at 1 m intervals, stem diameter determined at each end and sections were weighed green. Branches were removed and height, basal diameter, and length were measured on each branch. Branches were separated into foliated and unfoliated segments and weighed green. A stem disk and branch from each meter were returned to the lab to determine dry weight: green weight ratio. Foliated limb: foliage ratios were also determined from sub-sampled branches. Intensive culture resulted in larger growth differences for sweetgum (most intensive treatment 9.5 m tall, 13.1 cm DBH; control trees 5.0 m tall, 6.3 cm DBH) than in pine (most intensive treatment 10.3 m tall, 17.7 cm DBH; control, 7.6 m tall, 13.4 cm DBH). The pipe model of tree development explained dimensions of the upper 5 m of crown with leaf biomass highly correlated to branch basal area (r² from 0.697 to 0.947). There was a constant ratio of leaf biomass to branch basal area (50 gm/cm² for pine, 30 gm/cm² for sweetgum). We also found a constant ratio of bole basal area to cumulative branch basal area throughout the crowns. Rapidly growing pines produced about 49 Mg ha⁻¹ of stem biomass, 11 Mg ha⁻¹ of dead branch biomass, and 17 Mg ha⁻¹ of unfoliated branch biomass at the end of six years.     

Long-term yield potential of switchgrass-for-biofuel systems

Limited information is available regarding biomass production potential of long-term (>5- yr-old) switchgrass (Panicum virgatum L.) stands. Variables of interest in biomass production systems include cultivar selection, site/environment effects, and the impacts of fertility and harvest management on productivity and stand life. We studied biomass production of two upland and two lowland cultivars under two different managements at eight sites in the upper southeastern USA during 1999–2001. (Sites had been planted in 1992 and continuously managed for biomass production.) Switchgrass plots under lower-input management received 50 kg N ha⁻¹ yr⁻¹ and were harvested once, at the end of the season. Plots under higher-input management received 100 kg N ha⁻¹ (in two applications) and were harvested twice, in midsummer and at the end of the season. Management effects on yield, N removal, and stand density were evaluated. Annual biomass production across years, sites, cultivars, and managements averaged 14.2 Mg ha⁻¹. Across years and sites, a large (28%) yield response to increased inputs was observed for upland cultivars; but the potential value of higher-input management for lowland cultivars was masked overall by large site×management interactions. Nitrogen removal was greater under the higher-input system largely due to greater N concentrations in the midsummer harvests. Management recommendations (cultivar, fertilization, and harvest frequency), ideally, should be site and cultivar dependent, given the variable responses reported here.     

Comparison of the productivity of Populus nigra L. with an interspecific hybrid in a short rotation coppice in marginal areas

Populus nigra as an autochthonous European woody species is irreplaceable in regions where it is not legal to plant allochthonous species. Twelve clones of P. nigra ssp. nigra and one clone NE-42 (Populus maximowiczii×Populus trichocarpa) were tested in two localities at altitudes of 515–600 m with annual temperatures 5.7–6.8 °C. Different cultural practices and nutrition were used in these localities. Rooted plants were set out (2222 plants ha⁻¹). The second harvest was carried out after 4 years in a 7-year crop. The yield of the best clones of P. nigra (7.6–7.9 t ha⁻¹ yr⁻¹) approached the yield of hybrid clone (9.4 t ha⁻¹ yr⁻¹) in a fertilised locality, with pH=6.7 and lower rainfall amounts in the growing season. In a locality with pH=5, without fertilisation and with high groundwater level the yield of clones of P. nigra was 4.6–2.2 t ha⁻¹ yr⁻¹, in clone NE-42 it was 9.8 t ha⁻¹ yr⁻¹. The most productive clones of P. nigra had a significantly higher number of shoots (16.8–14.2) than the clone NE-42 (9.3) and the mortality of their shoots was lower (14–31.4%) than in NE-42 (32.1%). Shoots 20–53 mm in diameter accounted for 50% of the volume index of shoots in almost 70% of P. nigra clones. In high-yielding clones of P. nigra the dry weight of lateral shoots in total weight ranged between 66% and 75% while in NE-42 it was 55%. Resistance to Melampsora larici-populina Kleb. was higher in the interspecific hybrid but the best clone of P. nigra had a similar level of resistance.     

Above-ground biomass production and allometric relations of Eucalyptus globulus Labill. coppice plantations along a chronosequence in the central highlands of Ethiopia

Eucalyptus plantations are extensively managed for wood production in the central highlands of Ethiopia. Nevertheless, little is known about their biomass (dry matter) production, partitioning and dynamics over time. Data from 10 different Eucalyptus globulus stands, with a plantation age ranging from 11 to 60 years and with a coppice-shoot age ranging from 1 to 9 years were collected and analyzed. Above-ground tree biomass of 7–10 sampled trees per stand was determined destructively. Dry weights of tree components (W_c; leaves, twigs, branches, stembark, and stemwood) and total above-ground biomass (W_a) were estimated as a function of diameter above stump (D), tree height (H) and a combination of these. The best fits were obtained, using combinations of D and H. When only one explanatory variable was used, D performed better than H. Total above-ground biomass was linearly related to coppice-shoot age. In contrast a negative relation was observed between the above-ground biomass production and total plantation age (number of cutting cycles). Total above-ground biomass increased from 11 t ha^?1 at a stand age of 1 year to 153 t ha^?1 at 9 years. The highest dry weight was allocated to stemwood and decreased in the following order: stemwood > leaves > stembark > twigs > branches. The equations developed in this study to estimate biomass components can be applied to other Eucalyptus plantations under the assumption that the populations being studied are similar with regard to density and tree size to those for which the relationships were developed.     

Biomass yield,nitrogen response,and nutrient uptake of perennial bioenergy grasses in North Carolina

Although perennial grasses show considerable potential as candidates for lignocellulosic bioenergy production, these crops exhibit considerable variation in regional adaptability and yield. Giant miscanthus (Miscanthus × giganteus Greef & Deuter), Miscanthus sinensis Anderss. ‘Gracillimus’ and MH2006, plume grass (Saccharum arundinaceum Retz.), ravenna grass (Saccharum ravennae (L.) L.), switchgrass (Panicum virgatum L. ‘Alamo’), and giant reed (Arundo donax L.) field plots were established in 2008, treated with four nitrogen (N) fertilizer rates (0, 34, 67, 134 kg ha⁻¹ y⁻¹), and harvested annually in winter from 2008 to 2011. Giant reed, ‘Gracillimus’, switchgrass, MH2006, giant miscanthus and ravenna grass at the Mountain site produced mean dry matter yields of 22.8, 21.3, 20.9, 19.3, 18.4, and 10.0 Mg ha⁻¹ y−¹, respectively (averaged over the last two years). Dry matter yields at the Coastal site for giant reed, giant miscanthus, switchgrass, ravenna grass, and ‘Gracillimus’ were 27.4, 20.8, 20.1, 14.3, and 9.4 Mg ha⁻¹ y⁻¹, respectively (averaged over the last two years). Increasing N rates up to 134 kg N ha⁻¹ did not have a consistent significant effect on biomass production. High yields coupled with high mortality for plume grass at both sites indicates its potential as a bioenergy crop and need for continued improvement. Overall, the perennial grasses in this study had low nutrient removal, although giant reed and plume grass often removed significantly more N, P, K and S compared with Miscanthus spp. and switchgrass. Our results indicate that giant reed, giant miscanthus, and switchgrass are productive bioenergy crops across geographic regions of North Carolina.     

Above-ground biomass production and nutrient accumulation in young stands of silver birch on abandoned agricultural land

During the last decade, more than 400 000 ha of agricultural land was abandoned in Estonia. Such areas are often characterized by rapid natural afforestation with silver birch, which has led to an increase both in the woodland area and in the area of silver birch stands. However, many bioenergetic aspects related to birch stands growing on arable land are still poorly understood. The main aim of the present study was to investigate the above-ground biomass production, nutrient (NPK) accumulation, and foliar characteristics of young silver birch stands on abandoned agricultural land. Five 8-year-old stands of silver birch growing on different soil types were included in the study.The density of the studied stands varied from 3060 to 36 200 trees per ha and their above-ground biomass varied from 6.0 to 22.9 t DM ha⁻¹. The largest share in the above-ground biomass of the birches (59–80%) was from the stems. The mean stem mass of the birches ranged from 0.29 to 1.79 kg, and the mean total above-ground biomass ranged from 0.36 to 3.03 kg. The leaf area index for the studied stands varied from 1.21 to 4.64 m² m⁻², being the highest for the stand of medium density. Mean single leaf area varied from 9.4±0.2 to 15.4±0.3 cm², leaf weight per area varied from 61.1±0.4 to 77.5±0.5 g m², and specific leaf area varied from 13.2±0.1 to 16.8±0.1 m² kg⁻¹. However, no significant differences were found between stand density and the foliar characteristics. There was a strong positive correlation between soil nitrogen concentration and leaf nitrogen concentration (R=0.92); regarding phosphorus concentration, the corresponding correlation was weak (R=0.52) and regarding potassium concentration, no significant correlation was found. The amount of nitrogen accumulated in the above-ground part of the silver birch stands varied between 42.4 and 145.8 kg ha⁻¹, the amount of phosphorus, between 5.9 and 27.9 kg ha⁻¹, and the amount of potassium, between 7.2 and 78.6 kg ha⁻¹. The N:P:K ratios for the foliage were comparable. It is evident that the proportion of nitrogen and phosphorus are close to optimum, while the N:K ratio was lower than optimum value in all cases.     

Engineering,nutrient removal,and feedstock conversion evaluations of four corn stover harvest scenarios

Crop residue has been identified as a near-term source of biomass for renewable fuel, heat, power, chemicals and other bio-materials. A prototype one-pass harvest system was used to collect residue samples from a corn (Zea mays L.) field near Ames, IA. Four harvest scenarios (low cut, high-cut top, high-cut bottom, and normal cut) were evaluated and are expressed as collected stover harvest indices (CSHI). High-cut top and high-cut bottom samples were obtained from the same plot in separate operations. Chemical composition, dilute acid pretreatment response, ethanol conversion yield and efficiency, and thermochemical conversion for each scenario were determined. Mean grain yield in this study (10.1 Mg ha⁻¹ dry weight) was representative of the average yield (10.0 Mg ha⁻¹) for the area (Story County, IA) and year (2005). The four harvest scenarios removed 6.7, 4.9, 1.7, and 5.1 Mg ha⁻¹ of dry matter, respectively, or 0.60 for low cut, 0.66 for normal cut, and 0.61 for the total high-cut (top+bottom) scenarios when expressed as CSHI values. The macro-nutrient replacement value for the normal harvest scenario was $57.36 ha⁻¹ or $11.27 Mg⁻¹. Harvesting stalk bottoms increased stover water content, risk of combine damage, estimated transportation costs, and left insufficient soil cover, while also producing a problematic feedstock. These preliminary results indicate harvesting stover (including the cobs) at a height of approximately 40 cm would be best for farmers and ethanol producers because of faster harvest speed and higher quality ethanol feedstock.     

Utilization of summer legumes as bioenergy feedstocks

Sunn hemp (Crotolaria juncea), is a fast growing, high biomass yielding tropical legume that may be a possible southeastern bioenergy crop. When comparing this legume to a commonly grown summer legume – cowpeas (Vigna unguiculata), sunn hemp was superior in biomass yield (kg ha^?1) and subsequent energy yield (GJ ha^?1). In one year of the study after 12 weeks of growth, sunn hemp had 10.7 Mg ha^?1 of biomass with an energy content of 19.0 Mg ha^?1. This resulted in an energy yield of 204 GJ ha^?1. The energy content was 6% greater than that of cowpeas. Eventhough sunn hemp had a greater amount of ash, plant mineral concentrations were lower in some cases of minerals (K, Ca, Mg, S) known to reduce thermochemical conversion process efficiency. Pyrolytic degradation of both legumes revealed that sunn hemp began to degrade at higher temperatures as well as release greater amounts of volatile matter at a faster rate.     

A full economic analysis of switchgrass under different scenarios in Italy estimated by BEE model

Three different scenarios of switchgrass (Panicum virgatum L.) cultivation (high, mild and low) in two different environmental conditions (North and South Italy) were economically analysed by the computerized model BEE. The dataset was mostly generated from an 8.6 ha field of switchgrass planted in 2002 at the University of Bologna (North Italy). Annual equivalent costs (AEC) and break-even yield (BEY, i.e. the dry matter yield at which cost equals selling price) of each scenario were calculated to assess the feasibility of each scenario. AEC ranged from €511 to €1.257 ha⁻¹ being always higher in northern than southern regions. As expected, BEY varied to an extent depending on input levels. BEY was clearly higher under intensive cropping systems (H_S) compared to mild-(M_S) and low-input (L_S) scenarios. However, even for M_S or L_S, BEY generally exceeded the harvested yield. Therefore, we can conclude that, at the market price of €55 Mg⁻¹ (dry basis), switchgrass can be hardly grown both in North and South Italy. However, the biomass market price appeared surprisingly underestimated if compared to the unit energy price of crude oil, therefore a desirable increase of biomass price could be expected in the next few years. Sensitivity analysis showed that biomass price strongly affects BEY, and this was especially found in H_S. Furthermore, the differences in BEY between L_S and H_S clearly decreased with increasing market prices. Therefore, H_S could be better indicated than L_S at high market prices. Switchgrass was found to be more profitable than some conventional crops to an extent depending on the yield higher than BEY (Y_i). At the current biomass price, Y_i was from less than 1 Mg ha⁻¹ (maize and alfalfa) to more than 4 Mg ha⁻¹ (sugarbeet).     

Comparison of Arundo donax L. and Miscanthus x giganteus in a long-term field experiment in Central Italy: Analysis of productive characteristics and energy balance

Miscanthus x giganteus (miscanthus) and Arundo donax L. (giant reed) are two perennial crops which have been received particular attention during the last decade as bioenergy crops. The main aim of the present study was to compare the above-ground biomass production and the energy balance of these perennial rhizomatous grasses in a long-term field experiment. The crops were cultivated from 1992 to 2003 in the temperate climate of Central Italy with 20,000 plants ha^?1, 100–100–100 kg N, P₂O₅, K₂O per hectare, and without irrigation supply. For each year of trial, biomass was harvested in autumn to estimate biometric characteristics and productive parameters. Besides, energy analysis of biomass production was carried out determining energy output, energy input, energy efficiency (output/input) and net energy yield (output–input). Results showed high above-ground biomass yields over a period of 10 years for both species, with better productive performances in giant reed than in miscanthus (37.7 t DM ha^?1 year^?1 vs 28.7 t DM ha^?1 year^?1 averaged from 2 to 12 years of growth). Such high yields resulted positively correlated to number of stalks (miscanthus), plant height and stalk diameter (giant reed). Moreover, these perennial species are characterised by a favourable energy balance with a net energy yield of 467 and 637 GJ ha^?1 (1–12 year mean) for miscanthus and giant reed respectively.With such characteristics, both grasses could be proposed as biomass energy crops in Southern Europe with a significant and environmentally compatible contribution to energy needs.     

Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe

The energetic and environmental performance of production and distribution of the Brassica carinata biomass crop in Soria (Spain) is analysed using life cycle assessment (LCA) methodology in order to demonstrate the major potential that the crop has in southern Europe as a lignocellulosic fuel for use as a renewable energy source.The Life Cycle Impact Assessment (LCIA) including midpoint impact analysis that was performed shows that the use of fertilizers is the action with the highest impact in six of the 10 environmental categories considered, representing between 51% and 68% of the impact in these categories.The second most important impact is produced when the diesel is used in tractors and transport vehicles which represents between 48% and 77%. The contribution of the B. carinata cropping system to the global warming category is 12.7 g CO₂ eq. MJ⁻¹ biomass produced. Assuming a preliminary estimation of the B. carinata capacity of translocated CO₂ (631 kg CO₂ ha⁻¹) from below-ground biomass into the soil, the emissions are reduced by up to 5.2 g CO₂ eq. MJ⁻¹.The production and transport are as far as a thermoelectric plant of the B. carinata biomass used as a solid fuel consumes 0.12 MJ of primary energy per 1 MJ of biomass energy stored. In comparison with other fossil fuels such as natural gas, it reduces primary energy consumption by 33.2% and greenhouse gas emission from 33.1% to 71.2% depending on whether the capacity of translocated CO₂ is considered or not.The results of the analysis support the assertion that B. carinata crops are viable from an energy balance and environmental perspective for producing lignocellulosic solid fuel destined for the production of energy in southern Europe. Furthermore, the performance of the crop could be improved, thus increasing the energy and environmental benefits.     

Yield and composition of herbaceous biomass harvested from naturalized grassland in southern Iowa

Much of the land area in southern Iowa is used for perennial pastures that are dominated by cool-season grass species. These species are well adapted to the soils and climate and have become naturalized within the region. Biomass produced from these pastures might potentially be used as a feedstock for cofiring with coal to supplement supplies of dedicated energy crops such as switchgrass (Panicum virgatum L.). While much is known about the use of these pasture species for forage production, relatively little information is available on their use as a bioenergy feedstock. This research was conducted to assess the potential of harvesting cool-season pastures for cofiring with coal. Ten representative sites located in south central Iowa were evaluated. Across all sites, 26 plant species were identified, with individual sites having between 5 and 14 species. Biomass yield was determined at several sampling locations within each site. Yields ranged from 0.75 to 8.24 t ha⁻¹ over all sites. Mean yield across all sites was 4.20 t ha⁻¹. Fuel characteristics of the cool-season species were evaluated for burning qualities. Concentrations of ash, chlorine and sulfur are important for determining suitability in a biofuel. Ash content ranged from 58.5–118.1 g kg⁻¹ DM across all sites. Chlorine ranged from 0.8–7.6 g kg⁻¹ DM and sulfur content ranged from 0.7–3.4 g kg⁻¹ DM. Highest heating value (HHV) ranged from 17.69–19.46 MJ kg⁻¹. These results indicate that cool-season grassland in southern Iowa can produce biomass of sufficient yield and quality to supplement other sources for cofiring with coal to generate electricity.     

Cultivation of Spirulina platensis by continuous process using ammonium chloride as nitrogen source

This work is focused on the influence of dilution rate (0.08⩽D⩽0.32 d⁻¹) on the kinetics of continuous cultivation of Spirulina platensis at two different concentrations of ammonium chloride (N₀=1.0 and 10 mM) as nitrogen source. Cell productivity increased in both series of runs up to D≅0.12–0.16 d⁻¹, and then decreased. While at N₀=1.0 mM biomass washing was certainly the cause of progressive cell concentration decrease, a combination of this phenomenon with the toxic effect of excess ammonia was responsible, at N₀=10 mM and D⩾0.20 d⁻¹, for quick stop of cell growth just beyond the achievement of maximum cell productivity (92.4 mg l⁻¹ d⁻¹). Similar profile was observed for protein productivity, that achieved a maximum value of 67.0 mg l⁻¹ d⁻¹, because of the very high protein content (72.5%) of biomass produced under these conditions. The yield of nitrogen-to-biomass was much higher at the lower N₀, because of the low protein content, and reached a maximum value of 9.7 g g⁻¹ at D=0.08–0.12 d⁻¹. The yield of nitrogen-to-protein showed less marked difference, being most of the nitrogen present in the cell as proteins or free amino-acids.     

Long-term evaluation of biomass production and quality of two cardoon (Cynara cardunculus L.) cultivars for energy use

Cardoon (Cynara cardunculus L.) is an herbaceous species indicated as one of the most suitable energy crop for southern European countries. The aim of this work was to outline the productivity of two cardoon cultivars, Bianco Avorio (BA) and Gigante di Romagna (GR), over 11 years of cultivation in rain fed field conditions in the temperate climate of Central Italy. The quantitative and qualitative aspects of its biomass (calorific value, ultimate and proximate analyses, ash composition) as well as its energy balance (energy efficiency, net energy yield) have been determined. Crop dry yield was not different between the two cultivars and it was rather stable with a mean value (averaged from year 3 to 11) of 14 and 13 t ha^?1 for GR and BA respectively. Furthermore the biomass dry matter content was higher in BA than GR (51% vs 42%). The chemical analysis of cardoon biomass showed a similar composition in both cultivars with good calorific value (15 MJ kg^?1) but with an ash content (13.9% d.w.) higher than other herbaceous energy crops. The total energy input was higher in the establishing than in the following years, however from the planting year onward, both cardoon crops were characterised by a positive energy balance. Even if its mean net energy is lower than other perennial energy crops (182 GJ ha^?1 year^?1), cardoon can be easily propagated by seed with important advantages for crop management and production costs.The results confirmed cardoon's good biomass yield and favourable energy balance even in cultivation systems characterised by limited water input. Moreover future works are necessary in order to improve cardoon biomass quality and to evaluate the possibility of using it in blends with other biomass sources.